Camunda Modeler allows multiple incoming sequence flows for events after an event based gateway

[ingorichtsmeier]

Describe the bug

Since Version 5.5.1, the Camunda Modeler breaks the BPMN specification and allows multiple incoming sequence flows to an event that follows an event based gateway:

According to the BPMN specification this is not allowed (page 298 Business Process Model and Notation, v2.0):

Steps to reproduce

Create the model from above in Camunda Modeler 5.4.1 and 5.16.

In 5.4.1, you can not connect the events with an additional sequence flow:

Expected behavior

It should be impossible to connect both events in the latest version as well.

Environment

Impossible:
Camunda Modeler system information

• Version: 5.4.1
• Operating System: Windows 10 amd64
• Plugins: Cloud Connect, bpmn-js Token Simulation, Migration, Transaction Boundaries, Camunda Property Infos, Tooltip Plugin
• Execution Platform: BPMN - Camunda Platform 8

Possible:
Camunda Modeler system information

• Version: 5.16.0
• Operating System: Windows 10 amd64
• Plugins: bpmn-js Token Simulation, Camunda Property Infos, Tooltip Plugin, Transaction Boundaries, Cloud Connect, Migration
• Execution Platform:

Additional context

Maybe this issue happens in the BPMN-js library.

[nikku]

Cannot reproduce in Camunda Modeler v5.17.0:

Could you disable your plug-ins to verify these don't interfere?

[ingorichtsmeier]

It happens in the Web modeler as well. I found it there first.

[ingorichtsmeier]

In 5.16 without plugins it looks like in your screen movie and works as expected.

What breaks it in web modeler? (version: today).

Which plugin could influence it? Token simulation is available in both.

[nikku]

It seems like token simulation breaks it:

[marstamm]

I created bpmn-io/bpmn-js-token-simulation#139 in the token simulation repo. As this is not an issue in the desktop modeler itself, I am closing this issue in favor of the plugin issue.

We can consider opening an issue in the web-modeler for tracking, since we ship it there.